The requirements of the competitive sports have caused severe consequences in athletes involved in high level training. The changing in the aesthetic standards has leaded individuals to search for physical exercises to reduce their body mass, to increase their muscular mass as well as their aerobic fitness. It is quite common that athletes and non-athletes exceed the limits of their physical and psychological capacities causing the development of the overtraining syndrome, which is defined as the neuroendocrine disorder (hypothalamohypophysial), resulting from the imbalance between the demand of the exercise and the possibility of assimilation of the training, causing metabolic changes with consequences comprising not only the performance, but also other physiological and emotional aspects. The high level of physical, sociocultural and psychic stress are factors that contribute to such outcome, as well as to neuroendocrine changes caused by nutritional aspects that lead to serotoninergic fluctuations. Changes in the brain serotonin level can be associated to the occurrence of the physical fatigue, and this may be chronically settled, constituting one of the symptoms of the whole overtraining syndrome. Deficiencies or imbalances in neurotransmitters and neuromodulators can also be caused by severe or prolonged stress. The aim of this reviewing study was to analyze those factors that synergistically contribute to the outcome of the overtraining syndrome.